The subject of the invention is an elevator installation.
Elevator installations of the kind according to the invention usually comprise an elevator cage and a counterweight, which are movable in an elevator shaft or along free-standing guide devices. For producing the movement the elevator installation comprises at least one drive with at least one respective drive pulley, which, by way of support means and/or drive means, support the elevator cage and the counterweight and transmit the required drive forces to these.
In the following, for the sake of simplicity the support means and/or drive means are termed only support means.
An elevator system without an engine room is known from WO 03/1043926, in which wedge ribbed belts are used as support means for the elevator cage. These belts comprise a belt body of flat belt form which is produced from a resilient material (rubber, elastomer) and which has, on its running surface facing the drive pulley, several ribs extending in the belt longitudinal direction. These ribs co-operate with grooves, which are formed to be complementary thereto, in the periphery of driving or deflecting pulleys (termed belt pulleys in the following) in order on the one hand to guide the wedge ribbed belt on the drive pulleys and on the other hand to increase the traction capability between the drive pulley and the support means. The ribs and grooves have triangular or trapezium-shaped, i.e. wedgeshaped, cross-sections. Tensile carriers consisting of metallic or non-metallic strands are embedded in the belt body of the wedge ribbed belt and oriented in the belt longitudinal direction, which tensile carriers impart the requisite tensile strength and longitudinal stiffness to the support means.
The wedge-ribbed belts known from WO 03/043926 have certain disadvantages, i.e. they are not optimally adapted to the requirements of a support means for eleavtor cages. Such support means have to have a high load-bearing capability and a low longitudinal elasticity for smallest possible dimensions and smallest possible own weight and in that case be able to be guided over driving and deflecting pulleys with smallest possible diameters.
The wedge ribbed belts used as support means in accordance with WO 03/043926 exhibit, by comparison with the cross-sections of the tensile carriers, relatively large cross-sections of the belt bodies, i.e. the thickness of the belt bodies is large in relation to the diameter of the tensile carriers, and the edge regions, which face the pulleys and rollers, of the belt bodies, particularly the tips of the wedge-shaped ribs, are spaced comparatively far from the tensile carriers. In the case of the cross-section, which is given by the required load-bearing strength, of the tensile carriers this means that the disclosed wedge ribbed belts on the one hand have more than the absolutely necessary amount of material for the belt body and thus are too heavy and too expensive. On the other hand, the material of the belt body, which is relatively high in bending direction, is needlessly strongly loaded by alternating bending stresses when the support means runs around a drive pulley or a deflecting roller of small diameter, which can lead to formation of cracks and premature failure of the support means. In particular, the regions of the belt body spaced far from the tensile carriers, i.e. the tips of the wedge-shaped ribs, are exposed to strong alternating bending stresses.
The present invention is based on the task of creating an elevator installation of the aforedescribed kind in which the stated disadvantages are not present, i.e. that the elevator installation comprises a support means of flat belt form with ribs, which in the case of use with minimum belt pulley diameters and for a predetermined load-bearing capability has minimum dimensions and minimum weight, wherein the tensile carriers and the belt body are exposed to the smallest possible loads so that an optimum service life is guaranteed for the support means.
Pursuant to this task, one aspect of the present invention resides in an elevator installation having a support means of flat belt form which has at least on a running surface facing the drive pulley several ribs extending parallel in the belt longitudinal direction, wherein at least two tensile carriers oriented in the belt longitudinal direction are present per rib and the sum of the cross-sectional areas of all tensile carriers amounts to at least 25%, preferably 30% to 40%, of the total cross-sectional area of the support means. For ascertaining the total cross-sectional area of the tensile carriers, the cross-section defined by the outer diameter thereof is to be taken into account.
Through the distribution of the load to two tensile carriers (with the requisite cross-section) per rib it is achieved that the tensile means when the support means runs over belt pulleys with small diameters are exposed to smaller alternating bending stresses than if a single tensile carrier with correspondingly larger diameter were used per rib. With the indicated relationship between the sum of the cross-sectional areas of all tensile carriers and the cross-sectional area of the support means there is defined a support means which has optimally small dimensions and material quantities. The optimum small dimensions also have the consequence of correspondingly small alternating bending stresses in the material of the belt body. Materials (rubber, lastomer) can therefore be selected for production of the belt body which have a lower permissible bending stress, but tolerate higher area pressures between tensile carriers and belt body.
According to a preferred refinement of the invention there are used in the support means tensile carriers with a substantially round cross-section, the outer diameter of which amounts to at least 30%, preferably 35% to 40%, of the rib spacing. As rib spacing there is to be understood the spacing between adjacent ribs of a support means, which is usually the same between all ribs of a specific support means. In the case of a support means constructed in accordance with this rule it is ensured that the forces which are to be transmitted by the tensile carriers via the belt body to a drive pulley or a deflecting roller are optimally distributed in the belt body and the area pressures arising between tensile carriers and belt body are optimally small. The risk is thereby minimised that a loaded tensile carrier cuts through the belt body.
Advantageously the ribs have a wedge-shaped cross-section with a flank angle of 60° to 120°, wherein the range of 80° to 100° is to be preferred. The angle present between the two side surfaces (flank) of a wedge-shaped rib is termed flank angle. With flank angles of 60° to 120° it is ensured on the one hand that when the support means runs over belt pulleys no jamming between the ribs and the grooves, which are formed to be complementary thereto, of the belt pulleys arises. Running noises as also excitation of vibrations of the wedge-ribbed belt are thereby reduced. On the other hand, with such flank angles a sufficient guidance of the support means on the belt pulleys can be achieved, which prevents the lateral displacement of the support means relative to the belt pulleys.
An ideal distribution of the forces introduced from the belt body into the tensile carriers is achieved inter alia in that the spacings between the centres of tensile carriers associated with a specific rib are at most 20% smaller than the spacings between the centres of adjacent tensile carriers associated with adjoining ribs.
Optimally small dimensions and low weight of the support means are achievable if the minimum spacing of the outer contour of a tensile carrier from a surface of a rib amounts to at most 20% of the total thickness of the support means. The total thickness of the belt body with the grooves is to be understood as total thickness.
According to a preferred refinement of the invention the tensile carriers associated with a rib are so arranged that a respective outer tensile carrier lies substantially in the region of the perpendicular projection of each flank of the wedge-shaped rib. A projection oriented perpendicularly to the plane of the flat side of the support means is termed perpendicular projection and by “substantially” there is to be understood that at least 90% of the cross-sectional area of the respective tensile carrier lies within the said projection.
In the case of a particularly advantageous form of embodiment a respective outer tensile carrier is arranged entirely in the region of the perpendicular projection (P) of each flank of a wedge-shaped rib.
With the two arrangements, defined in the foregoing, of the tensile carriers in the flank region it is guaranteed that when running around a belt pulley no tensile carrier has to be supported by that point of the belt body which has the deepest notching formed by the grooves lying between the ribs.
In order to obtain support means which for a given tensile loading have a smallest possible longitudinal stretching, tensile carriers of steel wire cables are used. Steel wire cables are less stretched, for the same loading, than, for example, tensile carriers with the same cross-section of conventional synthetic fibres.
A support means with particularly low permissible bending radii, which is suitable for use in combination with belt pulleys of small diameter, can be achieved in that the steel wire cables have an outer diameter of less than 2 millimetres and are twisted from several wires which in total contain more than 50 individual wires.